Myeloproliferative stem cell disorders by deregulated Rap1 activation in SPA-1-deficient mice

Abstract

SPA-1 (signal-induced proliferation-associated gene-1) is a principal Rap1 GTPase-activating protein in hematopoietic progenitors. SPA-1-deficient mice developed a spectrum of myeloid disorders that resembled human chronic myelogenous leukemia (CML) in chronic phase, CML in blast crisis, and myelodysplastic syndrome as well as anemia. Preleukemic SPA-1-deficient mice revealed selective expansion of marrow pluripotential hematopoietic progenitors, which showed abnormal Rap1GTP accumulation. Overexpression of an active form of Rap1 promoted the proliferation of normal hematopoietic progenitors, while SPA-1 overexpression markedly suppressed it. Furthermore, restoring SPA-1 gene in a SPA-1-deficient leukemic blast cell line resulted in the dissolution of Rap1GTP accumulation and concomitant loss of the leukemogenicity in vivo. These results unveiled a role of Rap1 in myeloproliferative stem cell disorders and a tumor suppressor function of SPA-1.

Antigen-driven T cell anergy and defective memory T cell response via deregulated Rap1 activation in SPA-1-deficient mice

“…1 A). Ninety-five percent of SPA-1 Ϫ/Ϫ mice developed myeloid disorders by 16 months, with the initial signs becoming evident after 12 months (18). In the present cohort, SPA-1 Ϫ/Ϫ mice of various ages that showed no sign of the myeloid diseases by blood analysis and autopsies until 12 months and rare three 16-month-old mice without the diseases were used.…”

“…E14 embryonic stem cells were transfected with a linearized SPA-1 gene-targeting vector, in which a region covering exons 5-8 was replaced by a 1.8-kb fragment containing a pgk-neo cassette, microinjected into C57BL͞6 (B6) blastocysts, and the resulting chimeras were mated with B6 mice (18). Heterozygous offspring were intercrossed to produce homozygous mutant mice, and those with mixed genetic backgrounds were used.…”

“…SPA-1 is a predominant Rap1GAP expressed in the lymphohematopoietic tissues (16,17). Recently, we generated SPA-1 gene-deficient (SPA-1 Ϫ/Ϫ ) mice and found that they developed a spectrum of myeloid disorders that resembled human chronic myelogenous leukemia in the chronic phase, chronic myelogenous leukemia in blast crisis, or myelodysplastic syndrome (18). In the present study, we show that preceding the development of myeloid disorders, SPA-1 Ϫ/Ϫ mice develop an age-dependent progression of T cell unresponsiveness due to the antigen-driven increase in anergic T cells with large amounts of Rap1GTP.…”

BCR/ABL and IL-3 activate Rap1 to stimulate the B-Raf/MEK/Erk and Akt signaling pathways and to regulate proliferation, apoptosis, and adhesion

“…Both bone marrow preleukemic progenitors and overt leukemic blast cells in SPA-1/ mice showed markedly increased Rap1GTP levels, accompanied by a constitutive ERK activation. It was further demonstrated that the retroviral transduction of an activated mutant of Rap1, RapE63, into the normal bonemarrow progenitors significantly enhanced their expansion, whereas the overexpression of SPA-1 strongly suppressed it, confirming a positive role of Rap1 in proliferation of hematopoietic progenitors (Ishida et al, 2003). Intriguingly, in a leukemic cell line established from a SPA-1 deficient mouse with the disorder resembling CML in blast crisis, SPA-1 did not significantly affect the constitutive Erk activation and the proliferation rate, which were most likely due to constitutive activation of Ras, but abrogated the leukemogenic activity in vivo.…”

“…Most significantly, it was found that SPA-1-deficient mice developed myeloproliferative disorders resembling CML in chronic phase and in blast crisis (Ishida et al, 2003). Both bone marrow preleukemic progenitors and overt leukemic blast cells in SPA-1/ mice showed markedly increased Rap1GTP levels, accompanied by a constitutive ERK activation.…”